Method and apparatus for producing a well through a permafrost zone

ABSTRACT

A method and apparatus for producing a well in the earth through a zone of permafrost which is subject to subsidence on thawing, wherein casing is set in the permafrost subsidence zone and then allowed to subside at least one point along the length thereof with the permafrost.

United States Patent Inventor Appl. No,

Filed Patented Assignee Frank J. Schuh Dallas. Tex.

Nov. 5, 1969 Aug. 10, 1971 Atlantic Richfield Company New York, N.Y.

METHOD AND APPARATUS FOR PRODUCING A WELL THROUGH A PERMAFROST ZONE 10Claims, 1 Drawing Fig.

US. Cl 166/315, 166/67, 166/242, 285/144 lnt. Cl E21b 17/08, E2lb 33/04Field of Search 166/285, 288, 293, 313, 315, 57, 67, 75, 89, 242, 212;175/17;61/50; 285/133 A, 144

References Cited UNITED STATES PATENTS 5 12,513? 511935 Archer Humason285/144 Leman etal.... 285/144 Creighton 166/242 Hanes 166/242 Conrad166/212 Holmquist 166/242 Mullen 166/288 Scheinberg 61/50 Holmgren etal. 166/293 X Primary Examiner-lan A. Calvert Attorneys-Blucher S. Tharpand Roderick W. MacDonald ABSTRACT: A method and apparatus for producinga well in the earth through a zone of permafrost which is subject tosubsidence on thawing, wherein casing is set in the permafrostsubsidence zone and then allowed to subside at least one point along thelength thereof with the pennafrost.

PATENTED we 1 0 l9?! 3.598.184

V IN VENTOR FRANK J. SCHUH ATTORNEY METHOD AND APPARATUS FOR PRODUCING AWELL 7 THROUGH A PERMAFROST ZONE BACKGROUND OF THE INVENTION Permafrostis defined as a permanently frozen layer at variable depths below theearths surface in frigid regions. The permafrost layer is composed offrozen soil and rocks that may extend from near the earths surface tohundreds of feet there below. The upperportions of the permafrostcontain intervals of free ice and/or ice lenses. When the ice in thepermafrost is melted, the free ice and ice lenses can no longer supportthe soil and rock, thereby causing downward subsidence of the upperportion of the permafrost. In areas where the permafrost is thick, thisupper portion is correspondingly thick and therefore the zone ofsubsidence on thawing is potentially large.

When a well such as an oil well is drilled through the per- .mafrostlayer and produces oil or other liquid through the well bore, the oil orliquid being above the freezing point of water, a substantial amount ofpermafrost ice can be melted adjacent the well bore over the producinglife of the well. Thus, over the producing life of the well asubstantial amount of vertical permafrost subsidence can take place.

The well bore is normally lined with a pipe called casing and thefcasingis fixed to a wellhead structure at the surface of the earth.

when hot oil is produced through the casing in a thick permafrost zone,the ice in the permafrost adjacent the casing is melted along the fulllength of the casing in the permafrost zone thereby causing settling orsubsidence of the upper portion of the permafrost soil and rockdownwardly over several hundred feet of the casing in the permafrostzone. As the permafrost soil and rock settle downwardly, it is infrictional or drag contact with the casing and thereby tends to pull thecasing with it. Over the producing life of a well, the drag of thesubsiding permafrost can reach a magnitude such that the easing isdeformed to an extent that it fails and terminates production of thewell prematurely.

A layer of cement can be interposed between the casing and thepermafrost but this does not prevent melting of the permafrost ice andsettling of the permafrost soil and rock, nor does it prevent the casingand cement from being overloaded by the drag forces of the permafrostsubsidence to the point of casing failure.

SUMMARY OF THE INVENTION According to this invention, there is provideda method for producing a well in the earth through a zone of permafrostthat is subject to subsidence on thawing of the ice in the permafrost.The method provides, in its improvement, setting the casing in thepermafrost zone in contact with and/or exposure to thepermafrost andallowing at least one section of this casing to move with the permafrostas it subsides. Thus, one or more sections of the casing moves relativeto the remaining casing in the permafrost zone. The movement of easingwith the permafrost prevents excessive loading of the casing caused byfrictional contact of the casing with the subsiding per mafrost soil androck because the casing moves with and not against the subsidingpermafrost.

Also according to this invention, there is provided apparatus whereinthe casing in the permafrost zone is set in contact with and/or exposureto the permafrost and this casing carries at least one casing shearelement which includes means for allowing at least one section of thecasing to move relative to another section and shear means whichmaintains the movable casing section in a fixed position as set in thewell bore until a finite amount of permafrost subsidence has occurred.After the finite amount of permafrost subsidence has occurred, the shearmeans fails and allows relative movement of the casing sections therebyallowing the casing to move with the permafrost subsidence.

According to this invention the casing is employed in the permafrostsubsidence zone substantially without the use of an intermediate cementlayer so that substantially all of the casing is employed in directcontact with and/or direct exposure to the permafrost. No attempt ismade to isolate or insulate the casing from the permafrost.

Thus, this invention is useful in extending the producing life of a wellin geographical areas where permafrost is present and in which fluids attemperatures above the melting point of ice are produced from the wellthrough the permafrost zone to the earths surface.

Accordingly, it is an object of this invention to provide a new andimproved method and apparatus for producing a well through a permafrostzone. It is another object to provide a new and improved method andapparatus for extending the life of a producing well which produces forextended periods through a permafrost zone a fluid which is at atemperature above the freezing point of water. It is another object toprovide a new and improved method and apparatus for accommodatingpermafrost subsidence while producing a well through a permafrost zone.

Other aspects, objects, and advantages of this invention will beapparent to those skilled in the art from this disclosure and theappended claims.

DETAILED DESCRIPTION OF THE INVENTION The drawing shows a well structureemploying this invention.

More specifically, the drawing shows a combination I of well casing andwellheads, the casing extending from the earth's surface downwardly in awell bore 2 into a permafrost zone 3 that is subject to subsidence onthawing.

Permafrost zone casing 4 extends into well bore 2 and is directlyexposed to the sides of the well bore and therefore to the permafrost 3.

In this invention the term casing is meant to cover any pipe or otherconduit means which is employed as the liner for the well bore.Therefore, the casing is the outermost pipe in the well bore. Theoutermost pipe can be made up of two or more separate but concentriclengths of different diameter pipe. All of these pipe lengths areincluded within the term casing in this invention so long as they arethe outermost pipe and are in contact with the zone of permafrostsubsidence or are immediately adjacent said zone if not in contacttherewith. For example, large diameter pipe can be run from the earth'ssurface down, for example, 500 feet, after which smaller diameter pipeis run down the interior of the larger diameter pipe into a smaller wellbore. Both the smaller and larger diameter pipes are included within theterm casing" in this invention as long as both pipes are employed as theouter pipe of the well (through which yet smaller diameter pipes are tobe run) and so long as these pipes are the pipes nearest, if notcontiguous with, the zone of permafrost subsidence.

For the sake of brevity, the drawing shows only one string of casing forthe permafrost subsidence zone so that pipe 5. carried in the interiorof easing 4, can be producing easing and/or tubing or other suchconduits as required to complete the well but which is not exposed tothe zone of permafrost subsidence.

Casing 4 is fixed to its own wellhead 6 while pipe 5 is fixed to awellhead 7 which is separate from wellhead 6 and which is supported bypipe 5 (pipe 5 is fixed in the wellbore below the permafrost zone in aconventional manner).

When permafrost 3 subsides and moves casing 4 and its wellhead 6downwardly, wellhead 7 remains fixed in place notwithstanding themovement of wellhead 6. Thus, pipe 5 remains in position as casing 4moves downward with the permafrost.

Pipe Sis fixed to wellhead 7 by slip means 8. The slip means are carriedin ring 9 and have conventional teeth 10 that bite into the exteriorsurface of pipe 5. Slip means 8 or other obvious functional equivalentsthereof can be employed to prevent upward and/or downward movement ofpipe 5. For example,

the upper slip means can have teeth cut at an angle such that they biteinto pipe 5 in a direction that prevents pipe 5 from moving downwardwhile the lower slip means can have their teeth out in the oppositedirection so that they bite into the casing in a direction whichprevents pipe 5 from moving upward.

Wellhead 7 can carry a plurality of spacer means 11 such as the threadedbolts shown. Bolts 11 can be screwed downwardly through flange 7' ofwellhead 7 to come into con tact (abutting or threaded) with flange 6'of wellhead 6 after wellhead 6 has moved downwardly with the subsidingpermafrost. In this manner contact can be maintained between wellheads 6and 7 to rigidify the overall wellhead structure notwithstandingphysical separation of wellheads 6 and 7 with permafrost subsidence.

Casing 4 is provided with at least one casing shear element 12 which iscomposed ofinner and outer wall members 13 and 14, respectively. Whilemembers 13 and 14 are movable upwardly or downwardly relative to oneanother, they are fixed relative to one another to prevent free movementtherebetween by shear means 15. Shear element 12 is initially set in thewell bore as shown in the drawing, i.e., with wall members 13 and 14 ata known and preset position which is neither fully open nor fullyclosed. When the permafrost rock subsidence has occurred for a finitedistance thereby imposing an additional load on casing 4 which issufficient to cause shear means 15 to part or otherwise shear at theinterface between the adjacent surfaces of wall members 13 and 14, thesection of easing 4 above shear means 15 is free to move downwardly withthe subsiding permafrost thereby closing (shortening) shear element 12.It should be noted that it is possible for the sequence of permafrostsubsidence to be such .that one shear element 12 must lengthen while alower shear element is shortening to prevent excessive forces on thecasing 4.

Shear ring 15 extends into annular grooves in the outer surface of wallmember 13 and the inner surface of wall member 14. Other shear devicescan be employed. For example, pins, threads, welds, bolts, rivets, andthe like can be employed alone or in any desired combination as sheardevices.

The shear means can be made by physical design or chemical makeup orboth to give any desired strength while setting casing 4 in the wellbore thereby preventing parting of easing 4 while it is being handledand set in the well bore. In the same manner, the shear means can bemade to part to allow the upper section of casing to subside with thepermafrost rock after substantially any finite amount of permafrostsubsidence has occurred so long as the drag of subsidence is sufficientto overcome the strength of the shear means built thereinto to withstandhandling and emplacement of the casing.

A seal means can be provided between the adjacent faces of walls 13 and14 such as by O-ring 16 which is seated in an annular groove 17 in theouter surface ofinner wall member 13.

Element 12 is threaded at both ends 18 and 19 so that it can be insertedanywhere along the length of easing 4 between two sections of casingthat would otherwise be contiguous with one another. Thus, element 12 isinsertable in casing string 4 like a normal section of casing.

Since element 12 is emplaceable anywhere along the length of easing 4between adjacent sections of casing, a plurality of spaced-apartelements 12 can be emplaced along the full length of the zone ofsubsidence to minimize the drag forces on casing 4 between adjacentshear elements 12. If only a thin zone of permafrost subsidence isanticipated, a single element 12 can be employed. There is no maximumnumber of elements [2 that can be employed since they can be emplaced inthe casing stringjust like another section of casing and there fore canbe emplaced adjacent one another for any length desired.

The method of this invention thereby provides in its improvement settingof at least part of the casing in direct contact with and/or exposure tothe permafrost and allowing at least one section of the casing which isin contact with the permafrost to move relative, e.g., downwardly, tothe remaining section of the casing in response to permafrostsubsidence. This method prevents the casing from experiencing excessiveloading due to the permafrost subsiding while in contact with thatcasing.

Reasonable variations and modifications are possible within the scope ofthis disclosure without departing from the spirit and scope of thisinvention.

I claim:

1. ln a method for producing a well in the earth through a zone ofpermafrost that is subject to subsidence on thawing, the improvementcomprising setting a first casing in direct exposure to said permafrostzone, setting a second casing which is inside said first casing and notin direct exposure to said permafrost zone, said second casing beingfixed to the earth below the permafrost zone, both casings extending tothe earths surface and each carrying separate and freely separablewellheads, allowing at least one section of said first casing which isexposed to said permafrost zone to move longitudinally relative to theremaining sections of said first casing in response to downwardpermafrost subsidence thereby preventing said casing from experiencingincreased loading due to the permafrost subsiding downwardly while incontact with said casing, and separating said separate wellheads at theearths surface, the separation being effected by at least one section ofthe first casing moving downwardly with said per mafrost subsidence.

2. The method according to claim 1 wherein a plurality of spaced-apartsections of said first casing are allowed to move downwardly with thepermafrost subsidence.

3. The method according to claim 1 wherein said at least one movablecasing section resists downward movement until a finite amount ofpermafrost subsidence has first occurred.

4. ln apparatus for producing a well in the earth through a zone ofpermafrost that is subject to subsidence on thawing, the improvementcomprising first casing means set in direct exposure to said permafrostin said permafrost zone, said first casing means being fixed to a firstwellhead means, at least one casing shear element carried by said firstcasing means, said shear element including means for allowing onesection of said first casing means to move longitudinally relative toanother section of said first casing means, and shear means whichmaintains said first casing means in the position in which it is set inthe earth until a finite amount of downward permafrost subsidence hasoccurred after which and upon additional permafrost subsidence saidshear means fails and allows said relative longitudinal movement of saidfirst casing means section, second casing means inside said first casingmeans and not set in said permafrost zone, said second casing meansbeing fixed to the earth below the permafrost zone, second wellheadmeans fixed to said second casing means, said second wellhead meansbeing separate from and unconnected to said first wellhead means, saidfirst and second wellhead means being separable from one another toallow said first wellhead means to move downwardly with the subsidingpermafrost while said second wellhead means remains in place.

5. The apparatus according to claim 4 wherein a plurality of said shearelements are carried at intervals along the length of said first casingmeans.

6. The apparatus according to claim 4 wherein said shear elementcomprises inner and outer wall members which can move upwardly ordownwardly relative to one another and which are fixed relative to oneanother by said shear means so that there is no movement of said wallmembers relative to one another until said finite amount of permafrostsubsidence causes failure of said shear means.

7. The apparatus according to claim 6 wherein said shear means comprisesan annular ring fixed between said inner and outer wall members bygrooves in both said inner and outer wall members, said ring extendinginto the groove in each wall member.

8. The apparatus according to claim 4 wherein said casing carried bysaid second wellhead means is restrained from both upward and downwardmovement by slip means.

y 9. The apparatus according to claim 4 including movable spacer meansfor extending between and maintaining physical contact between saidfirst and second wellhead means when spaced apart.

10. The apparatus according to claim 9 wherein said spacer 5

1. In a method for producing a well in the earth through a zone ofpermafrost that is subject to subsidence on thawing, the improvementcomprising setting a first casing in direct exposure to said permafrostzone, setting a second casing which is inside said first casing and notin direct exposure to said permafrost zone, said second casing beingfixed to the earth below the permafrost zone, both casings extending tothe earth''s surface and each carrying separate and freely separablewellheads, allowing at least one section of said first casing which isexposed to said permafrost zone to move longitudinally relative to theremaining sections of said first casing in response to downwardpermafrost subsidence thereby preventing said casing from experiencingincreased loading due to the permafrost subsiding downwardly while incontact with said casing, and separating said separate wellheads at theearth''s surface, the separation being effected by at least one sectionof the first casing moving downwardly with said permafrost subsidence.2. The method according to claim 1 wherein a plurality of spaced-apartsections of said first casing are allowed to move downwardly with thepermafrost subsidence.
 3. The method according to claim 1 wherein saidat least one movable casing section resists downward movement until afinite amount of permafrost subsidence has first occurred.
 4. Inapparatus for producing a well in the earth through a zone of permafrostthat is subject to subsidence on thawing, the improvement comprisingfirst casing means set in direct exposure to said permafrost in saidpermafrost zone, said first casing means being fixed to a first wellheadmeans, at least one casing shear element carried by said first casingmeans, said shear element including means for allowing one section ofsaid first casing means to move longitudinally relative to anothersection of said first casing means, and shear means which maintains saidfirst casing means in the position in which it is set in the earth untila finite amount of downward permafrost subsidence has occurred afterwhich and upon additional permafrost subsidence said shear means failsand allows said relative longitudinal movement of said first casingmeans section, second casing means inside said first casing means andnot set in said permafrost zone, said second casing means being fixed tothe earth below the permafrost zone, second wellhead means fixed to saiDsecond casing means, said second wellhead means being separate from andunconnected to said first wellhead means, said first and second wellheadmeans being separable from one another to allow said first wellheadmeans to move downwardly with the subsiding permafrost while said secondwellhead means remains in place.
 5. The apparatus according to claim 4wherein a plurality of said shear elements are carried at intervalsalong the length of said first casing means.
 6. The apparatus accordingto claim 4 wherein said shear element comprises inner and outer wallmembers which can move upwardly or downwardly relative to one anotherand which are fixed relative to one another by said shear means so thatthere is no movement of said wall members relative to one another untilsaid finite amount of permafrost subsidence causes failure of said shearmeans.
 7. The apparatus according to claim 6 wherein said shear meanscomprises an annular ring fixed between said inner and outer wallmembers by grooves in both said inner and outer wall members, said ringextending into the groove in each wall member.
 8. The apparatusaccording to claim 4 wherein said casing carried by said second wellheadmeans is restrained from both upward and downward movement by slipmeans.
 9. The apparatus according to claim 4 including movable spacermeans for extending between and maintaining physical contact betweensaid first and second wellhead means when spaced apart.
 10. Theapparatus according to claim 9 wherein said spacer means comprises atleast one screw means carried by said second wellhead means, said screwmeans being threaded through said second wellhead means into contactwith said subsiding first wellhead means.